Rivers display Ge/Si ratios ranging from 0.3 to 1.2 × 10 -6, significantly lower than the average continental crustal composition ( Ge/Si= 1.3 × 10 -6) and do not, in general, display Ge/Si ratios reflecting that of the mineralogy in their drainage basins. In addition, seasonal changes in dissolved Ge/Si ratios are dramatic (a factor of 3). These observations suggest the operation of a bulk fractionation process(es) during weathering and transport of dissolved Ge and Si to the oceans which discriminates against soluble Ge. Buffering of Ge and Si by sorption onto riverine clays and surficial iron hydroxides may be important in controlling dissoved Ge and Si concentrations at Ge/Si ratios lower than crustal averages. The natural dissolved germanium to silicon ratio carried to the sea by rivers averages about 0.6 × 10-6 ± 10%.